• Only the leader can disband the alliance by clicking on the function button and then disband.
•  If the leader is offline for some time, the members can impeach him.
• The player can join one alliance. You must quit the current alliance if you want to join another one.
• You can leave the alliance by: 

Click on the alliance function button, then choose to leave the alliance.

Once you leave it, you can join another one.